Longest Palindromic Substring

Author: thanthtooaung-coding

Longest Palindromic Substring/README.md

@@ -0,0 +1,33 @@
+# Longest Palindromic Substring
+
+## LeetCode Problem
+- Problem Number: 5
+- Problem Link: https://leetcode.com/problems/longest-palindromic-substring/
+- Difficulty: Medium
+- Topics: String, Dynamic Programming
+
+## Problem Description
+Given a string s, return the longest palindromic substring in s.
+
+Note:
+- A palindrome is a string that reads the same forward and backward
+- A substring is a contiguous sequence of characters within the string
+
+## Examples
+
+### Example 1:
+```
+Input: s = "babad"
+Output: "bab"
+Explanation: "aba" is also a valid answer.
+```
+
+### Example 2:
+```
+Input: s = "cbbd"
+Output: "bb"
+```
+
+## Constraints
+- 1 <= s.length <= 1000
+- s consists of only digits and English letters

Longest Palindromic Substring/Solution.java

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+class Solution {
+    public String longestPalindrome(String s) {
+        if (s == null || s.length() < 1) return "";
+
+        int start = 0, end = 0;
+
+        for (int i = 0; i < s.length(); i++) {
+
+            int len1 = expandAroundCenter(s, i, i);
+
+            int len2 = expandAroundCenter(s, i, i + 1);
+
+            int len = Math.max(len1, len2);
+            
+            if (len > end - start) {
+                start = i - (len - 1) / 2;
+                end = i + len / 2;
+            }
+        }
+
+        return s.substring(start, end + 1);
+    }
+
+    private int expandAroundCenter(String s, int left, int right) {
+        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
+            left--;
+            right++;
+        }
+        return right - left - 1;
+    }
+}

README.md

@@ -16,13 +16,14 @@ Each problem has its own directory containing:
 | 2 | [Add Two Numbers](Add%20Two%20Numbers) | Medium | [Java](Add%20Two%20Numbers/Solution.java) | Linked List, Math, Recursion |
 | 3 | [Longest Substring Without Repeating Characters](Longest%20Substring%20Without%20Repeating%20Characters) | Medium | [Java](Longest%20Substring%20Without%20Repeating%20Characters/Solution.java) | Hash Table, String, Sliding Window |
 | 4 | [Median of Two Sorted Arrays](Median%20of%20Two%20Sorted%20Arrays) | Hard | [Java](Median%20of%20Two%20Sorted%20Arrays/Solution.java) | Array, Binary Search, Divide and Conquer |
+| 5 | [Longest Palindromic Substring](Longest%20Palindromic%20Substring) | Medium | [Java](Longest%20Palindromic%20Substring/Solution.java) | Two Pointers, String, Dynamic Programming |
 | 2924 | [Find Champion II](Find%20Champion%20II) | Medium | [Java](Find%20Champion%20II/Solution.java) | Graph |
 
 ## Categories
 
 ### By Difficulty
 - Easy: 1
-- Medium: 3
+- Medium: 4
 - Hard: 1
 
 ### By Topics
@@ -34,6 +35,9 @@ Each problem has its own directory containing:
   - [Longest Substring Without Repeating Characters](Longest%20Substring%20Without%20Repeating%20Characters)
 - String Problems
   - [Longest Substring Without Repeating Characters](Longest%20Substring%20Without%20Repeating%20Characters)
+  - [Longest Palindromic Substring](Longest%20Palindromic%20Substring)
+- Dynamic Programming Problems
+  - [Longest Palindromic Substring](Longest%20Palindromic%20Substring)
 - Linked List Problems
   - [Add Two Numbers](Add%20Two%20Numbers)
 - Math Problems